1. Field of the Invention
The present invention relates to modified hydrophilic polymers such as hyaluronic acid, also known as hyaluronan and mixtures thereof, containing hydrophobic silicone groups prepared by reaction of the hydrophilic polymer with epoxy-functional-silicones, their preparation and compositions containing them.
2. Description of Related Art
Relevant prior art includes the following references: U.S. Pat. No. 7,521,434 discloses cross-linked gels of hyaluronic acid with hydrophobic polymers and processes; Mensitieri et al. Journal of Material Science; Materials in Medicine (1994) pages 743-747; The rheological behavior of animal vitreus and its comparison with vitreal substitutes; and Schwarz, K. Proc Nat Acad Sci (1973) Vol 70 pp 1608-1612; A Bound form of Silicon in Glycosaminoglycans and Polyuronides.
Hyaluronic acid (HA) and its derivatives are important materials used in the medical and cosmetic industry. Their unique viscoelastic properties combined with their high water binding properties and exceptional biocompatibility have led to a wide variety of products in the ophthalmic, arthritis, wound healing, anti-adhesion, drug delivery, soft tissue augmentation, and burn management fields, as well as use in topical cosmetic moisturization. It is an excellent biomaterial for a variety of combined uses the medical field due to its viscoelastic and biocompatibility properties. The water binding and hydration properties of hyaluronic acid provide water to the skin. This moisturizing effect is widely used in the cosmetic industry.
Hyaluronic acid is a naturally occurring polysaccharide that consists of alternating N-acetyl-D-glucosamine and D-glucuronic acid monosaccharide units linked with alternating [beta] 1-3 glucoronidic and [beta] 1-4 glucosaminidic bonds. The molecular weight of hyaluronic acid is generally within the range of 50,000 up to more than 8,000,000
Hyaluronic acid is found in all vertebrates—in the skin, vitreous humor, the synovium, the cartilage, and the umbilical cord. It is not species specific and therefore highly biocompatible. It is known for its efficiency of hydration, it has a binding capacity of up to 20 times its weight in water and it is the natural moisturizer in the cell matrix of the skin. It typically exists at concentrations of 200 micrograms per gram of dermal tissue. Cross-linking of HA has been used to improve the physical properties of the molecule and to enhance its properties for various uses, or to immobilize the HA to various supports for medical purposes including the diagnosis of male infertility. Formulations of hyaluronic acid have been used by the cosmetic industry as skin moisturizers. One important use of hyaluronic acid and its derivatives is founded in its properties as a drug delivery vehicle. Various drug and other biological actives have been loaded into hydrogels of HA and its derivatives; however there are some limitations on the types of substances capable of being loaded based on their chemical nature. Hydrogels composed largely of water have difficulty accepting substances of hydrophobic nature. Some organic solvents used to solubilize a hydrophobic substance will dehydrate the hydrogel or precipitate the HA. Some methods have been developed to overcome this problem although there is still difficulty with some substances. Hyaluronic acid has been used for delivery of drugs such as diclofenac.
Silicones are also a very versatile class of compounds used for many applications in the medical field and cosmetic industry. Topical application of silicones have been used for wound healing, drug delivery and burn treatment and are also topically used in cosmetic formulations. Silicones are in general, hydrophobic and their moisturizing properties are due to their ability to provide a vapor barrier to the skin.
Silicone Gels are also used for delivery purposes in the medical field and the cosmetic industry. Their hydrophobic nature makes them excellent vehicles for incorporating hydrophobic substances. Silicone implants are used to deliver contraceptives and other hydrophobic drugs.